The synonyms of “support” are “back up”, “uphold”, and “sustain”.
“Back up” implies providing assistance or reinforcement from behind or in a secondary position. For example, “The evidence backs up his claim.” It shows that there is additional support given to strengthen an argument or position.
“Uphold” suggests maintaining or defending something. “The court is there to uphold the law.” It indicates a sense of standing by and preserving a principle, rule, or decision, which is a form of support.
“Sustain” means to keep something going or maintain it over a period of time. “The ecosystem needs to be sustained.” This implies providing the necessary resources or conditions to support the continued existence or operation of something.
In conclusion, these synonyms for “support” each have their own nuances but all convey the idea of providing assistance, maintenance, or reinforcement.